How Mette Gaarde uses light to measure ultrafast electrons

How do you measure things that move really fast? With light, of course! Dr. Mette Gaarde, Professor of Physics in the Department of Physics and Astronomy, explains how ultrafast pulses of light—think a billionth of a billionth of a second—can
be used to uncover very fast processes. We discuss how attosecond light pulses can
be applied to learn about electron movement in reactions along with what inspired
her to become a physicist. (Transcript below)

[0:01] This is Experimental, where we explore exciting research occurring at Louisiana
State University and learn about the individuals posing the questions. I'm Becky Carmichael,
and today we are joined by Dr. Mette Gaarde from the Department of Physics who explains
how ultrafast light can be used to uncover very fast processes.

Mette Gaarde

[0:20] Have you ever thought about what it takes to make a movie? Not organizing the
actors or designing the sets, but how the live action is actually captured. A movie
is generally a series of still pictures put together to show you how some event is
unfolding in time. For example, so you can see how the ball was passed from one player
to another. Each still picture needs to freeze the action, otherwise it will be blurry.
This means that the time to take the picture must be much shorter than the time it
takes for your object to move. For instance, if you want to freeze the wings of a
hummingbird, which beat really fast, like 50 times per second, there are two ways
to do this. You can use a camera with a really fast shutter mechanism. Or you can
put the hummingbird in a dark room and only shine light on it for a really short time,
like with a big flash, then your camera shadow can just be opened the whole time.
My research deals with how to produce and apply very, very short bursts of light that
can be used to make movies of things that move very fast. We're interested in the
motion of electrons inside atoms, molecules and solids. And these electrons moves
so fast that in order to freeze them, we need light pulses that only last a few 10s
of attoseconds. And I'm talking fast. One attosecond is a billionth of a billionth
of a second. For example, attosecond light pulses can help us watch the earliest steps
in a chemical reaction. And once we understand how those first steps take place, maybe
we can start to manipulate or control them. Or we could use attosecond light pulses
to learn about how the light harvesting process of a biomolecule works. Biomolecules
that absorb and convert UV light as part of the photosynthesis process. Attosecond
light pulses are made in laser laboratories in the US and around the world. My group
is a theory group so we do calculations to support and make predictions for these
experiments. For example, my Experimental collaborators may contact me about a measurement
that shows the attosecond light pulses behaving in some particular way. Then my job
would be to help them explain why that is. And maybe in the process of explaining
the behavior, we come up with new experimental tests that they could do in the lab.
One of the most fascinating projects I have been involved in recently is about the
generation of these light pulses in transparent crystals. Until just a few years ago,
this was thought to be impossible. It was believed that the high density of the material
in the solid state would make it too difficult for the light to make it out of the
crystal. However, recent experiments in theory have shown us that it is not just possible,
but that these light pulses can teach us a lot about how to rapidly control electric
currents in the solid state of matter. This is important because all electronic devices
rely on billions of microscopic currents being switched on and off every second. So
if attosecond science can help us control these currents, it may help us to dramatically
increase the speed of electronic signal processing.

Becky Carmichael

[3:34] So, hi. My name is Becky Carmichael, and I'd like to welcome Mette Gaarde today
to our show. So Dr. Gaarde, would you tell me a little bit about who you are and what
do you do here at LSU?

Mette Gaarde

[3:44] Right, so I am a professor in the Department of Physics and Astronomy, and
I am a theoretical physicist. As you have heard in my monologue, my research deals
with ultra fast processes. We are interested in things that happen on the shortest
timescales. And I do calculations that support experiments that deal with this kind
of physics.

Becky Carmichael

[4:08] So I was pretty impressed when you said the attosecond and that it's a billionth
of a billionth of a second. What drew you to this particular area physics,

Mette Gaarde

[4:19] I am fascinated by by things that happen in the time domain. I am fascinated
by the idea that you can watch things unfold, that you don't just know the beginning
and the end of some process, but you actually know... You can see how you get from
A to B. Was the ball thrown? Was it passed? Did it roll along the ground? But I think
also, to be honest, that I have been always influenced by the people around me that
I met. I would say I was not particularly inclined to study physics. But then when
I went to college, my first physics professor was an extremely fascinating person
and teacher and he would throw stuff around and he would twirl in the classroom and
he would show us basic laws of physics with everyday objects and with his body. And
I was tremendously fascinated. And so I stayed in physics. And I would say I was always
interested in atomic and molecular physics, because that seems like the perfect in-between.
It is not the very smallest scale, but it is also very closely associated with quantum
mechanics. But anyway, so I was kind of involved with a large group that was doing
atomic physics. And then the graduate program that I ended up in was in very much
the same way I went and visited this graduate program. And there was this crazy professor
who was, again, illustrating chirped pulse amplification by running around the conference
table, and I thought "I must work here". And then I didn't actually end up working
with that Professor, but I had a female professor who was my advisor in graduate school.
And she also made a huge difference for me staying in that program and kind of getting
me interested in and holding my interest because I think that's... Being a graduate
student is not just about being interested. It's also about that you stay interested
and you do the work that's necessary and that you keep going.

Becky Carmichael

[6:37] From those initial experiences, kind of that brought you into this area of
research. I also like that you're talking about how the methods of teaching that these
professors that you've encountered would use to demonstrate these processes? Do you
use any of those in your own classroom or for your own graduate students that you'd
like like to admit?

Mette Gaarde

[7:02] I do not believe I run around tables. No, I have not quite gone there. But
I'm certainly very aware of that physics needs to be conveyed with enthusiasm and
with examples, and in that the more concrete you can make things when you explain
them, the easier it goes over with students. So...

Becky Carmichael

[7:25] And the other piece that you had mentioned is the collaboration. So are there
any interesting collaborations that you've been involved with, or you're currently
involved with that help further the work that you're doing in your own lab?

Mette Gaarde

[7:40] Right. So I would say I have been tremendously lucky in being a theoretical
physicist and being allowed to work so closely with actually a number of different
experimental groups, which is just very enriching. When you can see that what I do,
which generally involves a computer and sitting in front of my computer, and talking
to my theory collaborators, and then that you see how this really works. I mean, it
really works in the lab, or you can help explain some experimental result and this
back and forth that we have between theory and experiment and to be involved so closely
in that. I have been very grateful to be involved in that.

Becky Carmichael

[8:26] So aside from, you know, having a solid understanding and keeping engaged with
the research happening with this area physics. Are there other skill sets that you
find that you've needed and you've employed during your duration as a faculty member,
as a graduate student, as a researcher?

Mette Gaarde

[8:46] If you're asking sort of about what would I tell a student who wanted to have
a career in physics, for example, I would say it's really important to dare to ask.
To stay curious. To not just take the answer for granted that you're given. To go
further. And sort of for a student in the classroom, I would also say don't be afraid
to not know the answer. I mean, most of the time, when you're a researcher, you don't
know the answer. There's a problem. And you know maybe how to get to the answer, but
you certainly don't know the answer when you start. And so don't be afraid to not
know. It's okay to ask.

Becky Carmichael

[9:31] You mentioned a little bit about an organization that you're involved with
for women in physics. Can you tell us a little bit about that?

Mette Gaarde

[9:38] Yes. So in the last four years, I have been involved with an organization that
puts on conferences for undergraduate women in physics, which is shortened to QWIP.
And this is a program that's run by the American Physical Society. And as you probably
know, there are very few women in physics. Not just in physics, but in many of the
STEM disciplines. But in particularly, in physics. There's only like 25% of women
at the undergraduate level. And this has been a problem for a long time and in many
different initiatives to try and get more women in physics. And so these conferences
are a series of regional conferences that happen to happen every year. They happen
during MLK weekend, where 100-200 undergraduate women get together at each of the
sites. Generally also with women professors, women industrialists, women physicists
who have made careers either, not just in academia, but used a physics degree to have
a career. And all these women get together, network, think about careers, think about
do they want to go to graduate school? Do they want to do an internship? Would they
like to do, you know... Would they like to go to business school? I mean, there are
many different things you can do with a physics degree. And we are trying to both
get these women together so that they can see they are not alone, but also to just
show them all the different things you can do with a physics degree. Because I think
most of you see your professors and you think that physics is about becoming a professor.
And it's not. There are lots of things you can do with a physics degree. And so I
have been very, very excited to be involved with this trying overall to make a difference.
Trying to convince more women to stay in physics, to enter physics, to have a physics
degree. It's exciting.

Becky Carmichael

[11:29] And so if someone's interested in becoming part of this organization, is there
a local chapter here at LSU?

Mette Gaarde

[11:36] So um, the conferences are primarily for physics majors or for students who
might have an interest in undertaking a physics major or a physics minor. They can
contact me if they're interested in attending next year, for instance. We would be
happy to have them. And there's also... Generally there is a society of physics students
who would be another another place to contact.

Becky Carmichael

[12:01] I want to step back to you for a minute, and I want you to think about yourself
when you were younger. Is there one thing if you could go back in time and tell your
younger self, what would it be?

Mette Gaarde

[12:12] Not to worry so much. You know, there are many different ways that things
can go right. And it doesn't all have to be... You can't imagine what's going to happen.
And so when opportunities arise, grab them. Just say, yes. Try it out. I would say,
yeah. Don't be afraid to be wrong. Don't be afraid to fail. You should try things,
and it might go better than you think.

Becky Carmichael

[12:42] I think that's also great advice. I think that there's some things that you
learn, even if it is... If it fails, it's okay. I think there's still things to grow
from. And so I think... I always liked this idea of grabbing opportunities, you never
know how that's going to change and fluctuate, or develop and grow that career path.
That's wonderful. Well, has there been something that I haven't asked you that you've
wanted to share kind of with students or with the community? Is there something that
we didn't really get to touch on yet?

Mette Gaarde

[13:12] We have talked about it a little bit. I mean, I think that physics is exciting.
I think that I wish more students would would share that excitement. I think a lot
of students think of physics is hard or oh, I need a lot of math to be a good physicist.
And eventually you do need to learn math to be a good physicist, but you can certainly
be excited by physics and be engaged in physics and be curious about physics and before
you have mastered a lot of complicated math. And I wish more students would share
our excitement about that, excitement about asking questions about the natural world
and how things work. That's what we work on.

Becky Carmichael

[13:55] Is there something or an example that you tend to lean on when you're trying
to share that enthusiasm with the students? Kind of your go to example. I know you
talked about, you know, to the ball, how did the ball move from point A to point B?
But is there some kind of example that you use that is very relevant for daily life?
I totally put you on the spot.

Mette Gaarde

[14:17] Yeah.

No. I don't think I have anything right out of the hat. No, I mean, let's, again,
let's move on.

Becky Carmichael

[14:23] I know. I'm sorry.

Move on from that one? Okay. I think I've asked you pretty much all the questions
that I had.

Mette Gaarde

[14:36] I mean, so what were some of the ones we skipped? One of them was "what do
you see yourself doing in the future?" I think this one is hard in the sense that,
you know, research is hard to predict, right? I mean, what am I doing if I'm doing
research in 10 years from now? That's very hard to say what... Where it's going. In
five years, maybe, we are thinking about... I can sort of see the horizon for where
the projects are going. 10 years? This is hard.

Becky Carmichael

[15:06] So then in five years, do you think... How do you see that your work is going
to contribute to that, that greater unknown? What is the piece that you see yourselves
to be uncovering?

Mette Gaarde

[15:16] Right, so I think that the last thing that I talked about in my monologue
about how to make attosecond light pulses in transparent crystals, I think this project,
not necessarily just my part of it, but I think the community is making huge steps
in that direction. How to control microscopic currents. How to understand microscopic
currents. And I think that the effort that's being done there in terms of sort of
controlling currents with light, controlling currents that could influence macroscopic
processes, I mean, inside of electronic devices, I think that could really be going
somewhere. Not necessarily just from my group, but from sort of a worldwide effort,
and I think that's very exciting to think about.

Becky Carmichael

[16:06] I think that that does sound very exciting. So I guess kind of going back
to the idea of those early stages of a reaction. I think that's very interesting in
terms of talking about kind of the energy that's transferred. Where's that energy
being... How can we harness that energy, maybe make it more efficient? Do you see
that that's something too?

Mette Gaarde

[16:27] I think, in general, all of this understanding leads to control. That's a
very general idea in my field that if you can map out how something happens, that's
the first step in learning how you can change how something happens. And change is
then a very general way of saying, Yes, I do not think that attosecond science is
going to change how bacteria perform photosynthesis. But I think maybe something much
more modest, that you can can change some fundamental step in some in some reaction.
Again, can you use light to control matter? That is really the fundamental question
that we're asking.

Experimental Podcast

[17:17] Experimental was recorded and produced in the KLSU Studios here on the campus
of Louisiana State University and is supported by LSU's Communication Across the Curriculum
and the College of Science. Today's interview was conducted by Becky Carmichael and
edited by Bailey Wilder. To learn more about today's episode, subscribe to the podcast,
ask questions, and recommend future investigators visit cxc.lsu.edu/experimental